A noise attenuating apparatus such as a muffler typically is used on noise sources to reduce the decibel levels or sound levels being generated thereby. For example, one common type of noise source is an internal combustion engine used on vehicles or power implements such as a lawn mower, snow blower, generator or the like. Such internal combustion engines typically generate noise at a high decibel level and a muffler is used on the engine exhaust. The muffler attenuates or reduces the sound levels to a level which is acceptable for an operator and/or the environment in which the noise source is being used.
For example, U.S. Pat. No. 4,415,059 (Hayashi) discloses a muffler for sound damping which has expansion chambers therein as well as additional chambers which surround the expansion chambers.
In a further example, U.S. Pat. No. 700,785 (Kull) discloses a muffler having a plurality of frusto-conical cones which are perforated to allow for the passage of the exhaust gases through the cones.
U.S. Pat. No. 2,919,761 also discloses a muffler having a plurality of expansion chambers which are separated one from the other by intermediate baffles that are formed with a plurality of orifices or openings therethrough so as to impose relatively little back pressure on the engine.
Additionally, U.S. Pat. Nos. 4,105,090 (Tachibana et al), 4,416,350 (Hayashi), 4,595,073 (Thawani), 4,635,752 (Jennings), 4,637,491 (Fukuda) and 5,378,435 (Gavoni) disclose further examples of mufflers.
While the above-identified prior art mufflers may be satisfactory for attenuating the sound levels generated by various internal combustion engines, the invention disclosed herein relates to an improved sound attenuating device which attenuates or reduces sound levels to an acceptable level while avoiding excessive increases in the back pressure on the medium or fluid being attenuated.
In particular, the invention relates to a noise attenuating device having a hollow housing through which the fluid being attenuated can flow. The housing includes an arrangement of tapered sound attenuators within the hollow interior which reduce the sound levels associated with sound waves and the fluid flow. The noise attenuating device of the invention not only reduces the sound levels but accomplishes the sound level reduction while providing a relatively large passage which extends along the length of the housing to allow the fluid to flow freely therethrough and avoid excessive increases in back pressure.
More particularly, the housing is axially elongate and has an inlet at one end thereof and an outlet at the other end thereof. The inlet is connected to the sound source such as an internal combustion engine for receiving the fluid flow and/or sound waves such that the fluid flow enters the interior chamber of the housing and passes therethrough to the outlet.
To reduce the noise levels associated with the fluid flow, the noise attenuating assembly preferably includes a diverter arrangement near the inlet end, and an inner cone or deflector assembly formed from a stack of tapered deflectors preferably formed as inner cones which extend axially between the diverter arrangement and the outlet. A longitudinal passage is defined in a radial space between the outer diameter of the inner cones and the inside of the housing so that the fluid can freely flow along the outside of the inner cone assembly.
To direct the fluid flow to the passage, the diverter arrangement includes a diverter cone which tapers outwardly away from the inlet so as to deflect the fluid flow and sound waves radially outwardly to the longitudinal passage. As a result, the fluid flow and sound waves travel along the length of the housing but radially outwardly of the inner cone assembly. Thus, unlike prior art mufflers which direct fluid flow through cones, the fluid in the inventive sound attenuating device primarily flows around the inner cone assembly along the longitudinal passage.
Attenuation of sound is accomplished by reflecting the sound waves within the housing. Accordingly, the inner cones are hollow and taper inwardly toward the outlet such that the larger base of the cones is open towards the inlet. The inner cones also are axially spaced apart to permit sound waves to be deflected into and around the hollow inner cones, which thereafter are deflected toward the housing wall and vice versa. Thus, the inner cone assembly primarily functions to deflect sound waves although some fluid flow may be permitted through the inner cone assembly.
To further assist in the deflection of the sound waves, the housing includes ring-like outer cones or tapered deflectors formed on the inside of the housing to reflect the sound waves towards the inner cones. Thus, as the sound waves enter the housing, the sound waves are reflected against the inner cone assembly.
The repeated or continuous deflection of the sound waves serves to reduce the sound levels wherein standing wave forms are believed to be created by the deflection of the sound waves. The standing wave forms interact with oncoming sound waves and cause a destructive interference or resistance therebetween which reduces the sound levels. Thus, while a relatively large passage is provided for the flow of the fluid through the muffler, the deflection of the sound waves off of the inner cone assembly serves to reduce the sound levels.
While the invention preferably is formed as a muffler for use with the exhaust or another flow of a fluid therethrough, the invention also is usable with additional sound sources which generate sound waves that travel into the housing.
Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.